1. Field of the Invention
The present invention relates to an automatic focusing system for a motion picture camera and more particularly to an automatic focusing system which utilizes the techniques of a laser radar and triangulation to adjust the lens for the distance between a moving or standing photographic subject and a camera focus plane in order to obtain very precise and accurate measurement of the distance so that the photographic subject is always maintained in focus.
2. Description of the Prior Art
Proper focusing of a motion picture camera is of critical importance in the commercial production of motion pictures. Sharpness of focus is an important consideration in the production of realistic commercially valuable films. Maintenance of a sharply focused image of the principal object of interest in a given scene, particularly when the principal object is in movement toward or from the camera, is a challenging matter in cinematography.
The concept of depth of field is a description of the range of distances an object of interest can be from the motion picture camera and still remain in acceptably sharp focus without adjustment of the camera lens. The depth of field becomes smaller with increasing lens focal length, with larger lens aperture and with decreasing object distance to the motion picture camera. There is a tendency in commercial camera work with a film or video camera toward a long focal length lens which is operated with a large aperture and at a close distance thereby producing a narrow limit on the depth of field. Under this narrow limit a precise and accurate adjustment of the lens focus is necessary. Previously a camera operator has depended on his skill to precisely and accurately adjust the lens focus.
U.S. Pat. No. 4,534,629, entitled Motion Picture Camera Automatic Focusing System, issued to Robert W. Bogle and Gary Gero on Aug. 13, 1985, and U.S. Pat. No. 4,601,557, entitled Motion Picture Camera Automatic Focusing System, issued to Robert W. Bogle and Gary Gero on July 22, 1986, teach an automatic focusing system for variable focus lens of a motion picture camera which includes a pulse modulator and a microwave transmitter which is mounted on a camera frame for generating a high frequency pulsed signal which is transmitted to a selected target which carries a reactive signal generator which is responsive to the first signal for coding and retransmitting the coded signal back to a receiver which is mounted on the camera frame, a signal processor for determining the interval of travel of the signal and translating the interval into a distance-analog signal that is transmitted to a focusing motor for driving the focusing mechanism of the lens for focusing the lens at the distance which is determined by the signal. The automatic focusing system is mounted on the housing of the motion picture camera.
U.S. Pat. No. 4,371,240, entitled Motion Picture Camera Having an Auto-Focus Adjusting Device, issued to Ichiro Shimizu, Yoshio Komine and Makoto Masunaga on Feb. 1, 1983, teaches an automatic focusing system for a motion picture camera which includes a servo motor with a shaft, a motor gear which is fixedly coupled to the shaft and a lens gear which is fixedly coupled to a lens barrel of a variable lens system and which engages the motor gear.
U.S. Pat. No. 4,611,244, entitled Auto-Focus System for Video Camera, issued to Kentaro Hanma and Toshio Murakami on Sept. 9, 1986, teaches an auto-focus system for a video camera having a zooming function. There is a discussion regarding the sufficiency of automatic focusing system for distances less than one meter. U.S. Pat. No. 4,191,460, entitled Camera with Automatic Focus Adjustment Device, issued to Makoto Fujiki on Mar. 4, 1980, teaches a camera having a zoom lens with a focusing range changeover device for selectively permitting photography in either one of ordinary zoom and macro-zoom modes. U.S. Pat. No. 4,719,485, entitled Automatic Follow-up Device for Camera, issued to Masao Shikaumi on July 12, 1988, teaches an automatic device for a camera which automatically captures a heat source, such as a human being, within a photographing field on the notion that a moving object to be photographed is often a human being.
U.S. Pat. No. 4,351,590, entitled Motion Picture Camera with Automatic Focusing Device, issued to Noritsugu Hirata, Masamichi Toyama, Hideto Iwama, Hidekazu Okajima and Akimasa Nishimura on Sept. 28, 1982, teaches a motion picture camera which has an automatic focusing device.
U.S. Pat. No. 4,294,531, entitled Auto-Focus Movie Camera, issued to Edwin K. Shenk on Oct. 13, 1981, teaches a motion picture camera which has a lens mount which is automatically positioned to maintain an image of a photographic subject in focus on the focal plane by generating periodic range pulses having a characteristic directly related to subject range and converting each pulse to a number which represents the focus position of the lens mount.
U.S. Pat. No. Re. 32,138, originally U.S. Pat. No. 4,082,436, entitled Motion Picture Camera, issued to Robert E. Gottschalk on May 6, 1986, teaches in a motion picture camera. U.S. Pat. No. 4,751,540, entitled Camera Tripod, issued to Mark D. Jones on June 14, 1988, teaches a tripod which is mounted on a motion picture camera. U.S. Pat. No. 3,924,828, entitled Pan, Tilt and Roll Tripod Head, issued to Victor R. Epperson on Dec. 9, 1975, teaches a pan-tilt tripod head with the added capability of rolling to either side to provide vertical or horizontal format for the motion picture camera. A single trigger controls all motion with the initial trigger squeeze releasing a clamp to allow pan and tilt motion and with a further trigger squeeze releasing a friction lock which allows the head to be rolled to either side. The trigger is mounted on a handle extended from the head for ease of control and the unit is adaptable to standard tripod and camera mounting attachments.
U.S. Pat. No. 4,268,137, entitled Radiation-Emisisve Focussing System with Integration of the Signal Produced by the System's Detector Arrangement, issued to Istvan Cocron, Theodor Huber and Wolfgang Ruf on May 19, 1981, teaches an automatic camera focusing system which has a transmitter and two detectors. The transmitter emits two pulses of radiation to a photographic subject which reflects the pulses of radiation onto the two detectors which provide a distance measuring signal to the automatic camera focusing system.